An electromagnetic bearing is a bearing which stably floats a rotor by an electromagnetic force with an axis position of the rotor being controlled by a control system. The bearing is generally called electromagnetic bearing or magnetic bearing and the most popular type in the related art is an active magnetic bearing (AMB). The electromagnetic bearing floats a rotor shaft at a special position by a magnetic force, thereby realizing functions of a traditional bearing, preventing the rotor from directly contacting with the bearing, dispensing with the lubricating and sealing, completely eliminating abrasion and reducing power consumption. The electromagnetic bearing has controllability, and the position of the rotor can be actively controlled and the rigidity and damping of the bearing can be adjusted by the control system. The electromagnetic bearing has the advantages such as a long work life, a large working temperature range and automatic balance. An electromagnetic bearing system is composed of four parts, that is, the rotor, a sensor, a controller and an actuator. The actuator includes an electromagnet, a power amplifier and so on.
Judging from the developments of magnetic bearings, many defects still exist. For example, all the core data and responses of the running of the magnetic bearing come from the position of the rotor, but an existing sensor which is used for determining a reference position of the rotor is usually apt to be disturbed by an adjacent electromagnetic field and an error of a sensor signal is usually a main reason for an emergent damaging breakdown caused on the magnetic bearing. However, because of the reasons such as a magnetic saturation property, an electromagnetic heating and so on of the material, the carrying capability of the electromagnetic bearing is limited.
A gas bearing is one type of mature bearing in the magnetic bearing technology and the gas bearing has a good self-adaptive property. The gas bearing can run for a long time in the condition of high temperature, high speed and high pollution, and because it does not need oil to lubricate and thus has a simple structure. Gas is used as a lubricating medium, therefore when the rotor is in a low speed running state, the gas bearing has a low carrying capability, and the damping and rigidity are also relative low, thereby causing a poor hot shutdown capability. Furthermore, in the start and stop stage, because the rotation speed of the gas bearing is decreased when the rotor starts and stops, thus causing a gas pressure to be insufficient in the shaft and a support force to be insufficient, and resulting in abrasion in the bearing which is unavoidable. Generally, both a sudden stop or a quick start of the gas bearing require an assistance of additional gas sources, after every start and stop are repeated for one time, a certain amount of using life is accordingly shortened and the reliability is caused to be decreased at the same time. The requirements of machining accuracy of structures and material of the gas bearing are very high and thus the application and development of the gas bearing are restricted and they are one of the main reasons that the gas bearing cannot be popularized in various industries with a low cost and a high reliability.
The gas magnetic hybrid bearing in the related art merely adds another set of complete magnetic bearing based on the structure and function of a set of complete static gas bearing. Generally, this method can only aim on increasing rotation accuracy. But the characters such as the production and maintaining cost and structure complexity are sharply increased instead, and thus the gas magnetic hybrid bearing can merely be a high price concept prototype and cannot be applied in large-scale industries.
For making up the defects of the gas magnetic hybrid bearing in the related art, a new gas magnetic hybrid bearing is expected. The working of a magnetic bearing is mainly used to correct the reference position between the bearing and the rotor. When a shock which is caused when the quality or accuracy of the gas bearing is not in a good condition, or a disturbance from outside makes walls of the rotor and a shaft sleeve to be in contact with each other, the rotor is actively drawn back by the magnetic bearing, thereby avoiding the touch between the rotor and the shaft sleeve and preventing an accident of journal sticking. The gas magnetic hybrid bearing can use a low cost sensor, decrease an electromagnetic disturbance and increase control efficiency. On one hand, the damping, rigidity and carrying capability of the magnetic bearing can be increased and on the other hand the defect that the gas bearing is hard to be controlled is also overcome.